Vinyl acetate-ethylene emulsions have been widely used as binders for, inter alia, paints, adhesives, and as binders for nonwoven and woven goods. The vinyl acetate-ethylene emulsions used for nonwoven goods generally contain a crosslinkable monomer, the crosslinking function being exercised after the emulsion is applied to a loosely assembled web of fibers. The crosslinking function serves to improve wet strength, dry strength, and solvent resistance in the goods.
Representative patents relating to vinyl acetate-ethylene emulsions and their use in various applications include:
U.S. Pat. No. 3,380,851 discloses a process for producing nonwoven fabrics by bonding together a loosely assembled web of fibers with the binder comprising an interpolymer of vinyl acetate-ethylene-N-methylol acrylamide where the interpolymer contains from 5 to 40% by weight ethylene and from 0.5 to 10% N-methlylol acrylamide by weight of the vinyl acetate. The emulsion is prepared by first forming a polymerization recipe of vinyl acetate, water, nonionic surfactant, reducing agent and, optionally, hydroxyethyl cellulose. The polymerization recipe is heated to a temperature of 50.degree. C. although broadly 0.degree. to 80.degree. C. and pressurized with ethylene to an operating pressure ranging from about 10 to 100 atmospheres with sufficient time being permitted for the ethylene to saturate the vinyl acetate. At that time the recipe is initiated by addition of oxidizing agent (catalyst) and polymerization effected until the vinyl acetate concentration falls below about 1% generally 0.5% by weight of the emulsion. N-methylol acrylamide is added incrementally to the reactor during polymerization, and it generally takes approximately 4-5 hours for such addition.
U.S. Pat. No. 3,498,875 discloses a process for producing bonded nonwoven fabrics in a manner similar to the '851 patent except that the interpolymer comprises vinyl acetate, ethylene and a crosslinkable monomer of glycidyl acrylate. The polymerization process is essentially the same as the '851 patent wherein the vinyl acetate and ethylene are initially charged to the reactor and the glycidyl acrylate added incrementally during the polymerization. Normally such addition is completed in about 2 hours or within 40 to 50% of the totally polymerization time.
U.S. Pat. No. 3,137,589 discloses a process for producing bonded fiber fleeces by using a binder consisting of a thermoplastic polyvinyl compound incorporating a crosslinkable monomer. The particular monomer used for effecting the crosslinking function is an N-methylol amide of acrylic acid or methacrylic acid or maleic acid. By and large the copolymers are acrylic type copolymers e.g. a mixture of butyl and methylmethacrylate and N-methylol acrylamide.
U.S. Pat. No. 3,081,197 discloses a process for producing nonwoven fabrics bonded with an interpolymer of vinyl acetate, 0.3 to 12% crosslinkable monomer, e.g., N-methylol acrylamide, glycidyl acrylate, glycidyl methacrylate or allyl glycidyl ether and an internal plasticizer of vinyl pelargonate or polyethylene glycol methacrylate and so forth. It is reported that the nonwoven fabrics have good wet strength and dry strength as well as water absorbency.
U.S. Pat. No. 3,708,388 discloses vinyl acetate-ethylene copolymer latexes having particular adaptability for lamination. The vinyl acetate-ethylene emulsion optionally incorporates a crosslinking monomer of the post reactive type and these include glycidyl vinyl ether, glycidyl methacrylate, N-methylol acrylamide. The process set forth in '388 patent is essentially the same as that in the '851 reference.
U.S. Pat. No. 3,844,990 relates to a paint composition comprising a vinyl acetate-ethylene copolymer latex having a cellulosic thickener. The vinyl acetate-ethylene copolymer latex contains from about 5 to 40% ethylene and is prepared in essentially the same manner in the '851 vinyl acetate-ethylene emulsions. The basic difference is that no crosslinkable monomer is employed.
U.S. Pat. No. 3,770,680 discloses a process for producing a grit free aqueous polymer emulsion particularly suited as a base for wood adhesive, the polymer comprising reaction product of vinyl acetate, N-methylol acrylamide and acrylic acid.
U.S. Pat. No. 3,404,113 discloses a process for producing an aqueous paint composition comprising a vinyl acetate-ethylene-triallyl cyanurate polymer latex where the ethylene concentration is from 5 to 40% and the triallyl cyanurate is incorporated in an amount from about 0.5-10%. The triallyl cyanurate can be added incrementally or added to the batch prior to initiation. Again, the polymerization procedure is much like that procedure described in the '851 patent.
U.S. Pat. No. 3,288,740 discloses a process for producing aqueous emulsions containing interpolymer having a crosslinkable function e.g. an N-methylol function. Generally the copolymers comprise a lower alkyl ester of acrylic or methacrylic acid in combination with N-methylol acrylamide or the ethers of N-methylol acrylamide.
British Pat. No. 991,550 discloses a process for producing emulsions of vinyl acetate and ethylene. A polymerization is carried out at a temperature of from about 50.degree. to 70.degree. C. at pressures from 10 to 100 atmospheres generally 20 to 60 atmospheres. The process for preparing emulsions differs generally from that of the '851 patent in that the vinyl acetate is added continuously during the reation period rather than being added initially to the recipe. The delayed addition of vinyl acetate permits greater incorporation of ethylene into the polymer.
The inventors are also aware of a process to produce vinyl acetate-ethylene adhesive emulsions having a Tg of about 15.degree.-19.degree. C. One initiates polymerization of a recipe of vinyl acetate, ethylene, water, stabilizer and reducing agent at a temperature of 25.degree. C. and a pressure below the operating pressure. The heat of reaction is utilized to achieve the operating temperature and operating pressure.